Another unbound local variable as seen in #1684

```
[2013-11-27 23:38:39,167: WARNING/Worker-1] /Users/jokey/.virtualenvs/sampleapp/lib/python2.7/site-packages/celery/app/trace.py:326: RuntimeWarning: Exception raised outside body: UnboundLocalError("local variable 'state' referenced before assignment",):
Traceback (most recent call last):
  File "/Users/jokey/.virtualenvs/sampleapp/lib/python2.7/site-packages/celery/app/trace.py", line 268, in trace_task
    retval=retval, state=state)
UnboundLocalError: local variable 'state' referenced before assignment
```